One known example of the prior art is an ultrasound diagnostic apparatus which can display a B-mode image representing echo intensities and a color flow mode image depicting directions and velocities of blood flows. This ultrasound diagnostic apparatus was constructed in such a way that it could display only the B-mode image or the color flow mode image of any given area, allowing an operator to specify a desired area in the B-mode image to present the color flow mode image within that area.